The present invention relates to pressure sensors and, more particularly, to capacitance-type pressure sensors.
Pressure sensors are used in numerous industries. One of the industries in which pressure sensors are especially pervasive is the aircraft industry. This is because aircraft pilots need to directly monitor various pressures, such as cabin pressure, atmospheric pressure, and turbine engine pressure. In addition, various other conditions that pilots need to monitor, or that the aircraft""s avionics system uses to control portions of the aircraft, use pressure sensors. For example, pressure sensors are used in systems that provide information about aircraft electronic turbine engine control, aircraft altitude, angle of attack, air speed, slip angle, and yaw angle, and turbine engine pressures. Thus, it is important that the pressure sensors used on aircraft be accurate and reliable.
A particular type of pressure sensor that has found widespread use in the aircraft industry is a quartz-constructed, capacitance-type pressure sensor. This pressure sensor type is particularly advantageous for aircraft applications because of its relatively low temperature coefficient of expansion, its nearly nonexistent hysteresis characteristics, its accuracy, stability and ruggedness.
However, this pressure sensor, while generally acceptable, when installed in its intended end-use environment, such as an aircraft, may exhibit certain drawbacks. In particular, when the pressure sensor assembly is exposed to varying external to internal differential pressure, the pressure sensor mounting hardware may deflect. Additionally, depending upon the particular end-use environment, the pressure sensor assembly may be exposed to varying vibratory forces. These deflections and vibrations may adversely affect sensor accuracy and may fatigue the electrical interconnections, which may cause pressure sensor failure.
Hence, to address these drawbacks, pressure sensors have been constructed to include a stress isolation component, such as a stem or an isolation diaphragm. The stem or isolation diaphragm are used to connect the pressure sensor to the mounting hardware, and additionally function to isolate the pressure sensor from the above-noted vibration stresses and deflections that the pressure sensor mounting hardware experiences.
Although using the stem or isolation diaphragm address the previously noted drawbacks, each presents its own disadvantages. For example, because the stem is mounted on an external circuit board, the stem-circuit board mount occupies component mounting area on the circuit board. Moreover, the housing into which the pressure sensor is installed should be sized to accommodate the stem. Both of these factors increase manufacturing costs and complexity.
Using the isolation diaphragm also results in increased manufacturing costs. The increased costs are associated with, among other things, the manufacturing steps for adding the isolation diaphragm to the pressure sensor. In particular, additional openings are provided through the isolation diaphragm to accommodate the sensor leads. These additional openings are processed by an additional annealing cycle to relieve the stresses associated with the formation of the openings. The isolation diaphragm is mounted by an additional laser welding operation. This process requires a significant amount of precision, and results in sensor scrap rates that are greater than otherwise desired.
Hence, there is a need for a rugged capacitance pressure sensor that overcomes one or more of the above-noted drawbacks. Namely, a pressure sensor that is sufficiently accurate when installed in its end-use environment, such as an aircraft, that does not require a special stem or isolation diaphragm and, therefore, is less expensive to manufacture.
The present invention provides an accurate, acceleration and vibration compensated capacitance pressure sensor that has a simplified structure, in that it includes no an additional stress isolation component.
According to an aspect of the present invention, and by way of example only, a pressure sensor includes a sensor portion, a support member, a base plate, and a plurality of electrically conductive flexible interconnect members. The support member is coupled to the sensor portion and includes a plurality of electrically conductive films on a surface thereof. The base plate includes a mounting surface coupled to the support member and a plurality of terminals passing therethrough. The plurality of electrically conductive flexible interconnect members are individually coupled between the plurality of electrically conductive films and the plurality of terminals.
Other independent features and advantages of the preferred sensor will become apparent from the following detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.